Acute exacerbations in chronic obstructive pulmonary disease (COPD)--microbial patterns and risk factors

Around 25% of patients with stable chronic obstructive pulmonary disease (COPD) show some evidence of tracheobronchial colonization. It is, however, probable that the vast majority of patients become colonized at some time during the course of the disease. A variety of factors including current smoking and viral infections predispose to bacterial colonization and subsequently acute exacerbations. In fact, infectious aetiologies account for around 50-75% of acute COPD exacerbations. Bacterial pathogens are present in around 50% of patients, Haemophilus influenzae and Streptococcus pneumoniae being the most frequently encountered pathogens. Pseudomonas aeruginosa and probably also Gram-negative enteric bacilli are more frequently found in patients with more severe airflow limitation. Viral infections are present in around 10-20%, with Influenzavirus representing the most frequent viral pathogen. Only recently, evidence for infection by Chlamydia pneumoniae has been found in 5-20% of patients. Predictors of distinct aetiologies have only infrequently been studied so far. Thus, it currently remains difficult to make adequate predictions on clinical grounds in the individual patient. Nevertheless, we would advocate to tentatively stratify the initial antimicrobial treatment according to the severity of the acute exacerbation episode and the presence of individual risk factors. The validation of such an approach may result in significant progress in our understanding of the role of infection and infectious agents in different subgroups of patients with acute exacerbations.